Due to the issues of energy resources and global climate change, and to promote the development of green energy and other alternative energy sources, the application of high-performance light source becomes more and more important. Therefore, recently the light-emitting diode (LED) used as the replacement of the existing fluorescent tubes has attracted more discussion options and become important applications. An electronic ballast with a high power factor (PF) or a traditional magnetic steel sheet ballast which needs a starter are severed as the power source of a fluorescent tube, however, the power source provided by the ballast can not be used directly on the DC light element, e.g., an LED. Therefore, a power transformation apparatus is required, for appropriate converting the power source supplied by the ballast, so as to provide the converted power source to the DC light elements such as the LED.
The ballast is an electrical apparatus, used for overcoming the negative-resistance characteristics of the gas-discharge light source, to make the gas-discharge light source to work successfully.
The gas-discharge light source, due to its discharge mechanism, usually has a negative-resistance characteristic in its normal working area: that is, as the current increases, the voltage decreases; vice versa. Therefore, if a gas-discharge lamp is connected to the voltage source directly, the gas-discharge lamp will be burned due to the current increased rapidly and exceeded the limit; the ballast hence must be used in series in the circuit to limit the current. Conventionally, the traditional ballast is an inductor formed by enameled wires entwined to an iron-core, and usually a starter is also needed to be used in conjunction with. On the other hand, the increasingly mature electronic ballast also gradually replaces the traditional inductive ballast.
The electronic ballast refers to the electronic apparatus which uses electronic technology to drive the electric light source, to produce the desired lighting. Because of its compact and lightweight, and the electronic ballast even can be integrated with the tube, more and more fluorescent tubes using electronic ballasts. The electronic ballast also has other functions, for example, by increasing the current frequency or changing the current waveform (e.g., into square waves), the discomforting flickers from the fluorescent tubes can be reduced or eliminated. Besides, the electronic ballast has a high power factor, which is higher than 0.95. In addition, other advantages of the electronic ballast include low-energy, small heat which can reduce the loading of the circuit and power consumption; low-noise, high-quality electronic ballast can has a noise under 35 db; the gas-discharge tube can be started successfully once when the gas-discharge tube is preheated, to avoid starting repeatedly, thereby extends the life of the gas-discharge tube; instant started without blinking, starter free; radiation is more stable, to help improving the visual resolution, to improve the effectiveness and reduce visual tiredness due to continuous operations, thereby help to protect human eyesight. In addition, the electronic ballast also maintains a constant power of the light source even if the large power/voltage deviation, to thereby keep a stable illumination, and is conducive to energy conservation. Therefore, the electronic ballasts have been widely used, and are gradually replacing magnetic steel sheet ballast which usually requires a starter.
As mentioned above, for promoting the energy efficiency of the fluorescent lighting, the electronic ballast having a high power factor has already replaced the magnetic steel sheet ballast (with a power factor about 0.65) which generally needs a starter; besides, since the LED with advantages such as good luminous efficacy and long usage life, the LED has become energy-saving light source. Therefore, it is a beneficial lighting scheme to use the electronic ballast with a high power factor in conjunction with the LED having a great lighting efficiency and a long usage life.
However, the output of the ballast is alternating current (AC), and the ballast is used to overcome the negative-resistance characteristics of the gas-discharge light source, so the ballast can not be connected directly to the LED that should be connected to a DC power source. In other words, an apparatus is needed to make the AC electric energy outputted from the electronic ballast to be converted as a valid and effective power source of the LED requiring a DC power source.
Recently, the main resolution of most methods is removing the electronic ballast, and using a power source converting module (AC to DC power module) to convert the applied AC power source to the DC power source; however, in this way, the usage life, efficiency and the cost are restricted due to the characteristics of the used elements, such as the switching elements (e.g., MOSFET), the output filter capacitor (e.g., the short life of the electrolyte of the electrolytic capacitor), and quality/size/cost issues of the transformer.
Therefore, it is an important issue to provide an apparatus and apply the apparatus in the existing lighting apparatus with the ballast. The apparatus can convert the electronic energy to the DC current for a DC lighting element, to make the provided apparatus can be worked with the various market-existing types of traditional or electronic ballast, and make the provided apparatus can be used to work with the power source supplied by a variety of ballasts without malfunction.